1. Field of the Invention
The present invention generally relates to video systems, and more particularly, to a chrominance processing arrangement for use in video systems that provides, among other things, immunity to colorstripe encoding.
2. Background Information
Techniques such as colorstripe encoding are often utilized to discourage the unauthorized reproduction of video recordings by degrading the quality of the resultant copies. Although colorstripe encoding is not intended to degrade playback of authorized video recordings, some picture degradation typically occurs. Colorstripe encoding software is commercially available from companies, such as Macrovision.
Colorstripe encoding generally involves inverting the polarity of a portion of the colorburst (i.e., “burst”) interval associated with a horizontal line of video information. Such encoding may be applied to a given number of horizontal lines that comprise a video frame. For example, colorstripe encoding may be applied to 4 out of every 20 lines, or to 2 out of every 17 lines, etc. The polarity inversion of colorstripe encoding causes the gain of automatic color control (“ACC”) circuitry of a video system to be modulated, thus resulting in horizontal stripes of oversaturated chrominance on the display.
A traditional approach for reducing the visibility of artifacts associated with colorstripe encoding is to make the ACC time-constant sufficiently large so that the amplitude of the modulation is reduced. This approach, however, is not completely satisfactory since it does not completely eliminate the artifacts, but simply reduces their amplitude. Moreover, this approach necessitates an ACC time-constant that may be larger than is otherwise preferred for optimum signal acquisition behavior.
Another approach for reducing the visibility of artifacts associated with colorstripe encoding is to utilize a burst replacement technique. In general, burst replacement involves stripping colorstripe encoding from video information by removing a burst packet and replacing it with an artificially generated burst packet. Burst replacement, however, is not ideal since removal of an original burst packet may cause valuable information within that burst packet to be lost, and thereby create operational problems within a video system. For example, removal of an original burst packet may cause chrominance synchronization problems to occur.
Accordingly, there is a need for a chrominance processing arrangement that avoids the aforementioned problems, and thereby provides improved immunity to colorstripe encoding. The present invention addresses these and other issues.